PROJECT SUMMARY/ABSTRACT Mutations in the breast cancer susceptibility protein, BRCA1, are heavily linked to the development of triple negative breast and ovarian cancer phenotypes. Currently, there are no precise treatments to mitigate the detrimental effects of BRCA1 mutations in triple negative cancer patients, and recurrence rates for this disease are higher than in any other form of breast cancer. In the nucleus, BRCA1 helps protect the genome by its involvement in DNA repair processes, thus serving as a tumor suppressor. However, cells harboring BRCA1 mutations lose the ability to properly repair DNA damage and transcribe their genome. The culmination of these events leads to genomic instability and eventually cancer induction. The precise manner in which mutated BRCA1 fails to execute its functions remains unclear. Understanding the molecular basis for these defects could provide significant insight toward developing new targeted therapies for BRCA1-related cancers. Based on our preliminary data derived from biochemical experiments, cryo-Electron Microscopy (EM) imaging, and molecular modeling routines, we believe differences in cancer development are related to morphological changes in the BRCA1 protein structure. Simply stated, mutations in BRCA1 that alter its structural elements will reduce its ability to engage other proteins during DNA repair. To investigate this idea at the subcellular level, we will utilize multi-scale imaging technology ranging from confocal microscopy to high-resolution cryo- EM. Combining this visualization information with rigorous biochemical analysis, we will develop a unique molecular-based approach to delineate the multifaceted role of BRCA1 in cancer formation. We also expect to define new opportunities to design targeted therapies based on mechanistic insights gathered at the molecular level of scientific inquiry.